“Golden” Cascade Cyclization to Benzo[c]‐Phenanthridines

Abstract

Herein, we describe a gold-catalyzed cascade cyclization of Boc-protected benzylamines bearing two tethered alkyne moieties in a domino reaction initiated by a 6endo-dig cyclization. The reaction was screened intensively, and the scope was explored, resulting in nine new Bocprotected dihydrobenzo[c]phenanthridines with yields of up to 98 %; even a π-extension and two bidirectional approaches were successful. Furthermore, thermal cleavage of the Boc group and subsequent oxidation gave substituted benzo [c] phenanthridines in up to quantitative yields. Two bidirectional approaches under the optimized conditions were successful, and the resulting π-extended molecules were tested as organic semiconductors in organic thin-film transistors.

Recent progress in the homogeneous gold-catalysed cycloisomerisation reactions

“…In 2021, A. Stephen K. Hashmi 47 and his group developed a protocol to prepare benzo[ c ] phenanthridine, which is an important class of alkaloids from N -boc protected benzylamine with a diyne chain using an Au( i ) catalyst (Scheme 39). Initially, the reaction was optimised with IPrAuNTf 2 and found to be the most suitable for this transformation.…”

“…This reaction was initiated with the formation of Au acetylide intermediate Int 68a, confirmed by a control experiment, from the activation of the alkyne moiety. An Au vinylidene In 2021, A. Stephen K. Hashmi 47 and his group developed a protocol to prepare benzo[c] phenanthridine, which is an important class of alkaloids from N-boc protected benzylamine with a diyne chain using an Au(I) catalyst (Scheme 39). Initially, the reaction was optimised with IPrAuNTf 2 and found to be the most suitable for this transformation.…”

Rhodium‐Catalyzed Intramolecular Cyclization and Rearrangement of 1‐Azido‐2‐(2,2‐Dihalovinyl)arenes and 1‐Azido‐2‐[(2,2‐Dihalovinyl)(Boc)amino]arenes for the Preparation of 2,3‐Dihaloindoles and 2‐Haloquinoxalines

“…Alternatively, electron transfer by decomposition of the Boc group is faster than the rearrangement of the bromo group, followed by aromatization (path b). [13] Next, the applicability of various aryl azides was investigated; the results are summarized in Table 3. For the 2,2-dichloro or 2,2-diiodovinyl(Boc)amino groups, the corresponding 2-haloquinoxalines 46 and 47 were also obtained (entries 1-3).…”

Modular synthetic strategies for dipyrrolopyrazines

“…Dye-sensitised solar cells utilising these dyes reached efficiencies ranging from 0.05% to 1.44% without the need for additives. 17,20 Our group later published a 4-step approach via a sequence of Sonogashira and Buchwald-Hartwig couplings, followed by gold(I)-catalysed [21][22][23][24][25][26][27][28][29] cyclisation affording N-phenyl-substituted dipyrrolopyrazines in an overall yield of up to 51% (Scheme 1). 30 Additional functionalisation was achieved by bromination of the pyrrolo-CH.…”

“…Our group later published a 4-step approach via a sequence of Sonogashira and Buchwald–Hartwig couplings, followed by gold( i )-catalysed 21–29 cyclisation affording N -phenyl-substituted dipyrrolopyrazines in an overall yield of up to 51% (Scheme 1). 30 Additional functionalisation was achieved by bromination of the pyrrolo-CH.…”